The invention relates generally to coating and extruding apparatus. More particularly, the present invention relates to coating and extruding apparatus that can be used to vary the transition rate of a fluid out of a die.
Using extrusion dies to form films and coating dies to coat a fluid onto a substrate is known. It is also known to coat a fluid onto a web in a series of discrete patches, or to extrude a film intermittently (e.g. onto a chilled roll). For example, one known way to coat intermittently onto a substrate is to use a flexographic coating process. Flexographic coating processes use rolls having raised surfaces that are pressed against a substrate. Each raised surface on the roll transfers a “patch” of coating fluid to the substrate. Using the flexographic coating process has many limitations. For example, in order to apply more than one type of fluid (e.g., different colors) to specific areas on a moving web requires a series of coating stations (typically requiring large rolls) with drying ovens positioned after each coating station. The fluids are typically applied by a coat/dry, coat/dry, . . . , coat/dry process. Thus, in order to coat multiple fluids multiple pieces of large expensive equipment must be used. Additionally, the repeat pattern on the roll determines the location of each patch of fluid and the spacing of the patches cannot be varied without changing the pattern of the raised surfaces or removing or replacing the rolls themselves. Thus, the overall repeat length of a patch series is limited and set by the circumference of the flexographic cylinders. Patch sizes cannot be changed except by changing the cylinders.
It is also known to provide a coating apparatus that has a main pump that provides the major supply of fluid to a coating die. Dosing pumps have been used to add and retract fluid in the die for starts and stops, respectively, of the coating process. In other words, the main pump provides a continuous supply of fluid to maintain a coating process and the dosing pump acts concurrently, adding or subtracting fluid to the die.
It is known to provide an apparatus for coating a pattern of spaced discrete patches on the web of material by using a metering pump that supplies coating fluid to the internal cavity of an extrusion (or coating) die from a fluid reservoir. The dies may also include a piston alone or in combination with a pump that can be translated into or out of the cavity to control the flow of fluid out of the extrusion/coating die. Typically, by translating the piston into the cavity of the die, material is translated out of the die (e.g., onto a substrate). Translating the piston out of the cavity typically stops translation of the fluid out of the die. One example of this concept are ram dies wherein the driving force for expelling the material from the die is provided directly by a long, thin piston positioned along the internal cavity of the die and along its width. These types of coating apparatus may also utilize a diaphragm, clamped so as to change the volume within a draw-in chamber when directly attached to a piston. The apparatus described above present the difficulty of providing for smooth motion of the piston or ram without contamination of the material being coated or extruded.